This invention relates to an electronic engine controller for controlling engine operations based upon various engine operating parameters and, more particularly, to a data sampling system for use in such an engine controller for synchronizing the A to D conversion of an analog signal indicative of engine load with engine rotation.
To achieve fuel economy, reduced unwanted exhaust emissions and improved engine performance and drivability, it is desirable to accurately control the various operations of an internal combustion engine such as spark timing, fuel metering and idle speed. Because of improved accuracy and lower costs, digital engine controllers have recently been proposed for controlling the various engine operations based upon existing engine operating parameters such as engine load, engine speed, engine coolant temperature, etc. A true indication of engine load may be obtained by the measurement of both engine speed and output torque, but a satisfactory sensor for measuring engine output torque is not available at this time. Because of this, it is the common practice to provide an inference of engine load by sensing the mass air flow into the engine or the absolute pressure within the engine intake manifold.
The measurement of mass air flow into the engine may be made by the use of an airflow meter such as a hot-wire airflow meter and a Karman's vortex shedding airflow meter which generates an analog signal indicative of mass air flow rate into the engine. The measurement of intake manifold absolute pressure may be made by the use of a pressure sensor including a piezo-electric element which generates an analog signal indicative of absolute pressure within the intake manifold. Such load sensors are very high in sensitivity and response to variations in conditions to be sensed. Thus, they are effective to sense transient engine operating conditions although they are sensitive to vacuum pulsations transmitted thereto under high load conditions where the engine is operated at or near full throttle. In order to avoid the limitations and drawbacks inherent in such load sensors, it is preferable to measure the average value of mass air flow rate into the engine or intake manifold absolute pressure over one intake stroke.
The analog signal indicative of engine load as inferred from measurement of mass air flow rate into the engine or intake manifold absolute pressure has to be converted into digital form for processing by a digital computer adapted to control the engine as a function of engine load. In the engine controllers of the prior art, the analog-to-digital conversion process is initiated, at predetermined intervals, on command from the digital computer. Thus, the converted digital value indicative of engine load does not represent the average value of engine load over one intake stroke. Particularly when the engine is operating at or near full throttle, large errors are introduced into the engine load measurement to cause improper fuel metering and spark timing control, spoiling fuel economy and exhaust emission purifying performance.
The present invention provides an electronic engine controller which can assure proper engine operation control so as to achieve fuel economy, reduced unwanted exhaust emissions and improved engine performance and drivability. The engine controller includes a data sampling system capable of sampling the value indicative of engine load in synchronism with engine rotation so that the sampled engine load value represents the average value of engine load over each intake stroke.